1. Field of Invention
The present invention relates to a fan and the controlling device thereof, and in particular to a fan and the controlling device thereof having the frequency of a rotation rate equivalent to the frequency of an alternating current power source supplied to the fan.
2. Related Art
Please refer to FIG. 1, which shows a control circuit of a motor of a conventional alternating current fan. The voltages of the alternating current power source is rectified and regulated by the bridge rectification circuit D1 and the capacitor (C1) to be high direct-current voltages. Then, the high direct-current voltages are supplied to the coil L1 and the coil L2 of the motor. However, when the motor is overloaded or the capacitance of the capacitor (C1) is too small, the voltage supplied to the motor will generate ripple fluctuation (as shown in FIG. 2A); and the ripple will be smaller when the load of the motor is not so heavy or the capacitance of the capacitor (C1) is large (as shown in FIG. 2B).
Moreover, the coil L1 and the coil L2 of the motor are electrified alternately in accordance with the frequency that the alternate magnetic poles (N pole or S pole) of the motor detected by the Hall sensor, and the frequency that the alternate magnetic poles of the motor detected by the Hall sensor is not equivalent to the frequency of the alternating current power, so that the voltages on the coil L1 and the coil L2 of the motor are shown in FIG. 3A and FIG. 3B, the surge voltage 5 is generated because of the inverse electromotive force of the inductance of the motor, this not only results in high temperature on the transistors Q1 and Q2 and the Zener diodes Zd1, Zd2, Zd3 and Zd4, but also make noises when the motor is rotating. Especially, as shown in FIG. 3C and FIG. 3D, the surge voltage 5 is more obvious when the load of the motor is heavier.